1. Field of the Invention
The present invention relates generally to a retention device, and particularly to a heat sink retention device including a back plate.
2. Related Art
Historically, when microprocessors were first commercialized, each microprocessor held less than one million transistors, and operated at speeds below 20 MHz. Typically, the microprocessors were either directly mounted to a printed circuit board by soldering or mounted to the printed circuit board via sockets.
With the continuing and rapid development of integrated circuits technology, the number of transistors contained in each microprocessor, as well as the processor operating speed, has increased dramatically. Correspondingly, the amount of heat that needs to be dissipated has increased. As a result, today's microprocessors used in computer systems almost employ heat sinks with fans to ensure that microprocessors run within their normal operating temperature ranges. At the same time, the trend to increase transistor density and operating speed is expected to continue. It is expected that because of increase of the amount of heat that needs to be dissipated, contact between the processor package and a heat sink will reach a point of critical importance. That is, the physical contact between the processor package and the heat sink plays a critical role in heat dissipation.
Heat dissipation efficiency of a heat sink has been increased by using a clip which physically holds the heat sink to firmly contact with the processor package. One such clip is a socket attach clip. To adequately dissipate heat from a processor containing large scale integrated circuits, a heat sink is required to have enough surface area. This results in an increased mass for the heat sink. Generally, the size of a socket is generally changeless, reliably retaining such an increscent large heat sink to the socket is difficult because of imparity of size between the heat sink and the socket. In order to mounting a large heat sink to a processor, a conventional method employs a spring clip with hooks to travel through mounting holes formed in the printed circuit board. The spring clip secures the heat sink to the processor after the hooks travel through the mounting holes to clasp the bottom face of the printed circuit board. An apparent disadvantage of this method is unsteadiness of mounting. The hooks are prone to jump out of the mounting holes due to mechanical shock or vibration during the operation of the processor, which results in the heat sink's departing from the processor and consequently the temperature of the processor's dramatically increasing. Another deflect also should not be ignored that the printed circuit board is prone to be damaged because of direct contacting force exerted by the spring clip, especially during mounting and removing the heat sink.
To overcome the above-mentioned deflect, an improved approach in which a plurality of rings is soldered to a circuit board has been developed. A clip with hooks for securing a heat sink clasps the rings instead of directly contacting the printed circuit board. However, it is required to affix extra structure to the printed circuit board. Furthermore, there is a requirement of adopting a solid metal material where the ring is soldered. On the other hand, a retention force between the heat sink and the printed circuit board could indirectly result in deformation of the printed circuit board as the increase of retention force for securing the heat sink along with the increase of volume of the heat sink.
At present, a prevalent approach, shown in FIG. 5, employs a back plate 100 which locates below a printed circuit board 200. A plurality of pillar 120 extends from the back plate 100 to pass through holes defined in the printed circuit board 200. A screw eye 121 is defined in the end of each pillar 120. Screws 400 corresponding to the pillars 120 travel through holes defined in a heat sink 300 to engage into the screw eyes 121 to thereby fasten the heat sink 300 onto a processor 220. The use of the back plate 100 avoids exerting a direct force on the printed circuit board and affixing extra construre to the printed circuit board. However, as any one skilled in the art has known, mounting a heat sink using screws is inconvenient, and making screw eyes in the pillars is not an efficient fabrication. A more dramatic disadvantage is that it is difficult to ensure the joining forces between the screws and the pillars in different place balance. Unbalanced joining forces will result in deformation of the printed circuit board and bad contact between the heat sink and the processor.
For the reasons stated above, and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for improved heat sink retention device.